A decline in European students’ interest in STEM subjects, exacerbated by the COVID-19 pandemic’s disruption of education, has raised concerns about the continent’s future workforce. To address this challenge, this study investigates the efficacy of the BIG GAME project methodology, a cooperative story-driven digital game approach designed to engage secondary students in collaborative environmental problem-solving. Implemented across Romania, Italy, Estonia, and Finland, this six-month study employed a mixed-methods design involving 62 teachers and 239 students in ten distinct game missions focused on environmental challenges. The quantitative results indicated significant improvements in students’ transversal skills (teamwork, communication, and critical thinking), as reported by over 75% of teachers. The qualitative data emphasised the value of structured peer review in developing students’ reflective practices. This research underscores the importance of teacher facilitation in game-based learning and problem-based simulations and highlights the potential of such methodologies to boost student engagement and environmental awareness. These findings suggest that the BIG GAME project approach could be a valuable tool for revitalising STEM education and cultivating future-ready citizens.